As a conventional technique, an ultrasonic flowmeter using the ultrasonic pulsed method has been known as disclosed in Japanese Unexamined Patent Application Publication No. 2000-97742.
The ultrasonic flowmeter has a configuration wherein ultrasonic pulses are cast from a transducer onto a measurement line within a flow tube, ultrasonic echo signals, i.e., the reflected-wave signals from suspended fine particles in a fluid flowing in the fluid tube are analyzed so as to calculate the flow-speed distribution and the flow of the fluid flowing along the measurement line based upon the positions and velocities of the suspended fine particles. The measurement line is formed by an ultrasonic-pulse beam cast from the transducer.
The ultrasonic flowmeter may be applied to an opaque fluid and an opaque-fluid tube, as well as having the advantage of measuring the flow of a fluid flowing a fluid tube in a non-contact manner. Furthermore, the ultrasonic flowmeter has the advantage of measurement of the flow-speed distribution of an opaque fluid and the flow thereof, e.g., measurement of the flow of liquid metal such as mercury, sodium, and so forth, as well as having functions for measuring the flow-speed distribution and the flow of a fluid flowing in the flow tube with measurement along the measurement line.
The ultrasonic flowmeter has the advantage of detecting change in the flow-speed distribution over time along the measurement line formed by the ultrasonic pulses cast onto the fluid from the transducer, and accordingly, it is hoped that the ultrasonic flowmeter can be applied to measurement of a transient flow of a fluid flowing through the flow tube, and measurement of the flow-speed distribution and measurement of the flow in a turbulent situation.
An arrangement example of the ultrasonic flow-speed distributor and the ultrasonic flowmeter described above is disclosed in Japanese Unexamined Patent Application Publication No. 2000-97742 (see Patent document 1, for example).
[Patent document 1] Japanese Unexamined Patent Application Publication No. 2000-97742.
With a conventional ultrasonic flowmeter utilizing ultrasonic pulses, in the event that a fluid tube for guiding a fluid to be measured in which a great number of ultrasonic reflectors such as fine particles and bubbles are suspended is a metal tube, noise called clutter noise which is present constantly (regardless of time) is superimposed on an ultrasonic echo signal, which prevents the flow-speed distribution and flow of a fluid from accurate and high-precision measurement.
The present invention has been made in light of the above situation, and it is an object of the present invention to provide an ultrasonic flow-speed distributor and flowmeter, an ultrasonic flow-speed distribution and flow measurement method, and an ultrasonic flow-speed distribution and flow measurement program, which are capable of sufficiently reducing the noise level as to ultrasonic echo signals, and measuring flow-speed distribution and flow precisely, even in the event that noise, which is constantly present, such as clutter noise is superimposed on ultrasonic echo signals.